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Re: Cap materials
Subject: Re: Cap materials
Date: Thu, 17 Apr 1997 14:26:24 -0700
From: Gary Weaver <gweaver-at-earthlink-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
> Gary Lau wrote:
> >
> > I'm about to start building some rolled poly caps, and have a question
> > about sourcing materials. .09" thick polyethelene is not commonly
> > available, but .006" thick is. Is it reasonable to use 16 layers of
> > this thin stuff, or would this many layers be totally unwieldy?
> >
> > I don't have access to a vacuum pump to pump the cap down to remove
>the bubbles. Would the multi thin layers pose a greater problem in
> > harboring air bubbles?
> >
> > Also, for the mineral oil, what kind of place does one go to for this?
> > Auto supply store?
> >
> > Gary Lau
> > Waltham, MA
>
> Gary,
>
> A number of thin sheets of dielectric is better than 1 or two
> thicknesses of thicker material. The flat plate caps I use each 4 mil
> thick material, since this was very easy and economical to get. 8 layers
> are used per plate cap, and 4 caps are tied in series to yield a total
> thickness of 132 mils. 96 mils is probably more than adequate for even
> 15 KV Neon use as long as you make sure you've eliminated most of the
> air between the layers. I originally was going to make rolled caps out
> of this material, but trying to wind the multiple thicknesses proved to
> be very frustrating, and totally unsuccessful. A couple of coilers have
> reported success making rolled caps from stacked layers of this stuff,
> but a high degree of skill and patience is warranted (and I lacked a
> sufficient amount of either! : ^) ).
>
> If you orient the materials so that the plates are vertical, air can
> escape naturally over a period of time, especially during a lower
> voltage break-in period in Tesla Coil use. This lets you get by without
> needing a vacuum pump.
>
> Mineral oil can be purchased at Veterinary supply places, drug stores,
> and petroleum products dealers. Local utilities also use this oil for
> transformers, and will often sell you some (or even give you some).
> Transformer oil brand names include Shell Diala-X or AX, Exxon Univolt
> 60, Esso Voltesso 35. For Tesla Coil caps, pure USP mineral oil, like
> Tulco Lubsnap 100, Shell MVI-65, or USP Veterinary Grade will work just
> fine. Even baby oil will work - and it smaells alot nicer that Diala-AX!
> Some coilers have even used plain old SAE 10 or 20 weight engine oil,
> but
> this often contains additives that may degrade its perfomance in Tesla
> Coil capacitors. Let your fingers do the walkin' in the Yellow Pages -
> you should be able to find a number of sources - go with the cheapest
> one!
>
> Safe cappin' to you!
>
> -- Bert --
My New Capacitors. I spent several weeks thinking about this before I
finally decided to build it. All of the capacitor plans I
have seen look hard to build thats why I have refused to build one. I
came up with my own design that seem easy to build.
Also with other plans I have seen you can not use the new capacitor for
several months until all the air has had a chance to
escape. With my design you do not have to wait to use the new
capacitor.
I bought a roll of .010 aluminum flashing 10" wide at the lumber yard.
I cut the cap plates 9' long with a 12" long tab that is
1.5" wide. The total length with the tab is 10'. I used a paper punch
to make a hole in the tab so I could bolt is down. I
folded the tabs over 90 degrees so it will stick out on the side of the
plate and stick out the end of the caps after it is rolled up.
I bought a roll of .006 mill clear polyethylene at the lumber yard. The
roll was 10' by 100'. I cut it into strips 14" wide by
222" long by rolling the plastic around a pipe first then cutting around
the pipe with a razor knife. I laided the strips out on the
carpet floor in the house. I put 9 layers of poly in a stack. Then I
laid the aluminum plate on the stack of poly and folded the
poly over the top of the aluminum plate. Now there is 9 layers of .006
poly on both sides of the plate. Its made like a
sandwich with poly on both sides and the aluminum plate in the middle.
The poly hangs over each side of the plate 2" and
hangs over the tab end 3".
I made 2 poly and aluminum sandwitches and placed one on top of the
other making sure that one tab sticks out on the left
side and the other tab sticks out on the right side. The tabs are on
the open end of the poly not the end where the poly folds
around the plate.
I bought a piece of 1" PVC pipe to use as a center for rolling the
plates up tight. The 1" pipe measures 1.25" outside diameter.
I cut a piece of 1" pipe 15" long for the center. I placed the 1" pipe
on the end of the poly that folds around the plates not the
tab end of the plate and started rolling. I rolled it up as tight as I
could. The sheet of poly tried to get out of line a little on both
sides but with a 2" hang over this is not a problem. I put a piece of
masking tape around the rolled cap to hold it in place until I
could insert it into the 6" PVC pipe. After rolling both plates
together there are 18 layers of .006 mil polyethylene between
each plate. d=.108 A=1080 K=2 C=.00896 uf 40,000 volt rating.
Formula C=[(.224 times K times A) divided by d]
times 2.
I cut a piece of 6" PVC pipe 16" long and slid the rolled capacitor into
the pipe. It was a very tight fit. I had to spin the
capacitor in the direction of the roll after I removed the tape to get
it to go into the pipe all the way.
I drilled a # 7 hole in the PVC end caps and tapped the plastic for 1/4"
by 20 threads. I made 2 threaded studs 2" long from
1/4" threaded rod and screwed the stud into the threaded hole of the end
cap. Then I put a 1/4" hex nut on each end of the
stud and tightened it against the plastic end caps. I put a small
amount of lock tight on the threaded rod and nuts to hold them
in place. I used the hot melt glue gun to seal around the hex nuts
where they touch the end caps. I drill and tap a 1/8" NPT
pipe thread in only one end cap. I made sure there was 1/2" of thread
sticking out on the outside of the cap for wire
connections and a nut.
Next is put the aluminum tabs from cap on the 1/4" threaded rods and put
on a lock washer and a nut to hold it in place. Then
I glued the end caps to the 6" PVC pipe with lots of glue and used a
rubber hammer to make sure they were on all the way.
While the glue was drying on the PVC I drove to the power company and
bought 5 gallons of transformer oil for $2.00 a
gallon. When I returned home about an hour later I connected the
vacuum pump to the 1/8" pipe threads on the end cap of
the capacitor and pumped a vacuum. The vacuum guage was reading 30. I
held the vacuum for a few minutes then closed the
valve to the pump and opened the valve to the container of oil and back
filled the capacitor. It took a few minutes for the cap
to fill with oil. Then I removed the vacuum hose and plugged the hole
with a socket set screw pipe plug.
Construction time and cost of 1 rolled capacitors .008 uf. 2 aluminum
plates 25 minutes $6.00.
18 polyethylene sheet 14" by 222" 45 minutes $9.20. 2 PVC end caps 6"
dia drill and tap. 5 min $20.46. 1
PVC pipe 6" dia by 16" 5 min $3.18. Misc, nuts, washer, stud, pipe
plug. 5 min $1.00. 1 gallon of
transformer oil 10 minutes $2.00. 1 PVC pipe 1" dia by 15"
long 2 min $0.30. TOTAL
construction time = 87 min each cap $42.14 each cap.
I spent more time driving around town buying the materials than I did
building the capacitors. I probably spent 5 or 6 hours
driving around town getting the stuff together to make these capacitors.
I tested the finished capacitors and they are .0103 uf rated 40 KVA.
Sence then I have made other capacitors.
Plate dementions.
.01 uf plates = 10" x 108" long. Fits perfect in a 6" PVC pipe.
.005 uf plates = 10" x 54" long. Fits perfect in a 4" PVC pipe.
.0025 uf plates = 10" x 27" long. Fits perfect in 3" PVC pipe.
Use 9 layers of .006 mil polyethylene for all 3 capacitors. Make sure
the poly hangs over 2" all around the egdes.
Gary Weaver